


The Complete Guide to Xenobiology

by teaandcharcoal



Category: Homestuck
Genre: Alien Biology, For Science!, Troll Biology, Xeno, Xenobiology
Language: English
Status: Completed
Published: 2013-12-04
Updated: 2013-12-15
Packaged: 2018-01-03 11:45:24
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 7
Words: 9,811
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1070087
Author URL: https://archiveofourown.org/users/teaandcharcoal/pseuds/teaandcharcoal
Summary: <blockquote class="userstuff">
              <p>Exactly what it says on the tin: I try to create a logical and (mostly) complete guide to troll biology. Comments and criticisms are welcome.</p>
            </blockquote>





	1. Evolution

Notes

The author of this work would like to begin with a disclaimer and an apology. The disclaimer first: I am not a biologist. I don't even have a bachelor's degree. I am, however, studying for said degree and am enrolled in a university to obtain such an expensive piece of paper. In fact, this is being written in order to help me review topics for my upcoming comparative physiology final. As such, I will be going through most major body systems. This work was made by combining Homestuck canon, my limited knowledge of entomology, my headcanon and human physiology. The facts taken into account for this guide are weighted in that order. Any suggestions, corrections, or comments are very much welcomed.

Now for the apology: this work is not as politically correct as it could be. My reasoning stands as follows: the terminology I use in my work ought to be as close as possible to that in the work which I am studying (Vander's Human Physiology as a text along with the lectures from my professor who shall remain nameless for this moment). In addition, it allows for clarity of language. I am well aware that it is somewhat problematic and cissexist to use the words "male" and "female" in referring to all individuals within a species sharing certain physical traits, and the issue likely worsens within species that are hermaphrodidic. That being said, these words serve as important shorthands in science, and my task is large enough as things stand. I apologize if this offends or triggers anyone, and I suggest that you stop reading. Please note, however, that I acknowledge and respect all genders. I simply must be wary of word count.

I treat blood castes in the same respect, as one of Kankri's speeches leads me to believe that trolls exist who do not identify with the caste into which they were born. However, I doubt any trolls are actually reading this, so I am not as concerned. If you are a troll, please let me know, as I am clearly quite curious about your culture and biology.

Introduction

When I first got into Homestuck, the thing I found most interesting was Alternian life. Andrew Hussie has created a wide world, full of science and functional magic before the introduction of the trolls. The world of Homestuck is too big and broad to possibly be explored, even in such a long work. Also, it seems likely to me that Hussie lacks the knowledge and drive to do so. Therefore, the task of fleshing out this beautiful multiverse falls to the fans.

I myself have been a fan of world-building for many years, and as someone interested in biology I immediately latched onto the trolls and how they work. It seems to be fate that a few short months after I first became interested in Homestuck I stand close to completing a class in comparative physiology. Using this newfound knowledge, I seek to explore the facets of troll biology. This work will be split into several chapters for ease of reading. I shall be posting updates as I complete each of these chapters.

I am doing my best to be wary of my grammar and spelling, but I am working against the clock to have this finished by my final for the class and do not have a beta. As said earlier, all suggestions and questions are welcome. Also, should you find something you like, feel free to use it in your stories or drawings or whatever! This is, of course, not a definitive work and is endorsed by absolutely no one except for me.

I hope you enjoy this, and find the information compiled as interesting as I do.

Chapter 1 – Alternian Evolution

The first step when looking at any form of comparative biology is to trace evolutionary trees. This gives us a better understanding of when and why structures formed the way that they did. Based on the mother grub, wigglers, and a general bug theme I am led to believe that trolls have evolved from arthropods. More specifically, because of the structure of the mother grub and wigglers, I have pinned them as splitting off from Hexapoda (insects).

I've named their taxa, which has grown to be dominant on Alternia, Hussia for obvious reasons. The defining features of Hussia are pigmented blood and over-sized mushroom bodies (explained in the chapter on the nervous system). There are two major groups within Hussia: lusia and trollia.

Members of the former are known as lusus naturae, named such because slight genetic changes in this taxa create huge phenotypical diversity, many traits of which are not observed in other taxa anywhere on Alternia. Lusia is itself then broken into two smaller groups: sinistarus and familiarus. Members of Sinistarus are creatures such as musclebeasts and other "wild animals." Much more research has been done on Lusia Familiarus. There are a total of 50 recorded species of Lusia Familiarus, one for each of the 48 existing castes, one for limebloods, and the one to which Karkat's lusus belongs. (actually, the reverse is more correct: the hemospectrum is continuous, but Lusii only choose trolls whose blood matches their own, and those who are off-spectrum or simply not close enough are left to die or killed by the lusus themselves). More on them (especially on the Mother Grub, which is one of these species) will be covered in the chapter on reproduction near the end of the work (I might also do a snippet on the Vantases at some point).

Though lusia cannot be ignored, trolls serve as the focus of this text. Much like the hominid group on Earth, there were once many more species of troll. This genus is defined by speech abilities, the hemospectrum, and having an internal skeleton as adults. Modern trolls are more scientifically known as trollia Spaien Modernae. Though fossil and archeological evidence of other troll species are rare, there are clear differences in skull shape and size, and there are also hypothesized reproductive differences.

I may draw a tree of this later.

It is important to note in Alternian evolution that deuterostomes (the group containing Echinoderms and Chordates) never evolved. All resemblances to these groups are either the result of convergent evolution or the force of Paradox space in order for the universe to propagate itself (Paradox space allows for the disregard for parsimony in some cases. Because, let's be real here, the odds of creating humanoid, sentient, two-gendered species, that share body language, and John Cusack in three universes are pretty damn low, even by evolutionary standards in which the odds of anything are absurdly bad. So the existence of universal constants is important). Frogs actually evolved from mollusks in this world. Don't ask me how. It's just a thing.

The species of Hussia most closely fill the role that mammals do on modern day Earth. Because of evolving to fill those niches, along with the universal constants of Paradox Space, Trolls are most easily compared to Humans. Therefore, the same names for hormones and certain chemicals that share functions shall be used, even if they are slightly different. Other things, such as hemoglobin, are actually identical. It's a mixed bag. Also, human names for structures shall be used until reproduction is reached at the end of this work.


	2. Nervous System

**Notes for the Chapter:**

> I have not proofread this, but my final is in a week so I'm just like gogogogogo. As stated before, questions and suggestions are very much appreciated!

On the most basic level, trolls have very similar nervous systems to humans. Their neurons are nearly identical, which is quite logical considering the conservation of this type of cell throughout many taxa on earth. The exception to this rule is that that they have the neurotransmitter octopamine instead of the norepinephrine found in humans, keeping with their insect ancestry (however, it is not currently believed that this difference is what accounts for the inability for psychic powers to properly effect humans. More on that later).

Adults also have what is, in effect, a spinal chord. However, it is important to note that in the larval stage this is a ventral nerve chord, as other insects do. During pupation, the ganglia along their chord (think very separated and non-specialized. For my entomologists out there, think Dictyopterus. For my non-etymologists out there, google “insect ganglia.” It’s the one with all the lumpies down the line instead of the one fused at the top) become coated in chitin with cartilage forming between the chitin sections. During the next few sweeps, the spine (along with other internal chitin structures) slowly calcify so that by the time the young troll is five sweeps old they have a full bony skeleton.

The most obvious difference to a human studying the nervous system of trolls would, in fact, be the brain. While the behavioral and cognitive results are fairly similar, it becomes clear that they took a different evolutionary pathway to reach them. The most obvious of these upon dissection would be the apparent lack of a cerebellum and traditional brainstem. However, this is not a question of what one is looking for and is instead one of _where_ they are looking for it. Like all insects, what we would consider a brain is split into super- and suboesophageal ganglia (which they describe as “fore- and hind brain.”) What this means is that instead of having their centers for coordination and involuntary reactions (breathing, heart rate, blood pressure, etc.) at the base of their skull as humans do, it is instead located in their chest near to the heart, where it is protected by the ribcage, surrounding organs, and a thick layer of fluid. (In most insects it’s a little closer than that, but most insects also don’t have necks, so there you go). So, fun facts, it would _technically_ be possible to keep a troll alive (as in, able to have normal bodily functions) without a head, assuming they were somehow kept from bleeding to death and given nutrients and water through an IV. Why one would want to do such a thing is another question entirely.

The forebrain is interesting for an entirely different set of reasons. They have fairly similar structures to those of humans for sight, smell, and taste, along with a (very small) structure for controlling movements of the head and neck near the base of the brain. However, the bulk of their brain is comprised of tightly-packed mushroom bodies (little structures that, as the name suggest, look like mushrooms. These are responsible for memory and social aspects in insects and also happen to have some genes homologous to those in the human forebrain). Upon first inspection (especially as they too have several layers of connective tissue for filtering blood and preventing brain contamination), these are easily mistaken for the folds of our brains. However, this is a clear case of convergent evolution, the result of trying to pack as many neurons in the skull as possible. Some of these near the very front of the brain appear to be slightly different in shape (a bit flatter and broader). It is not known, but these are believed to have to do with psychic abilities.

In another case of convergent evolution (possibly in the agenda of Paradox space), they have a highly specialized region in the center of their brain believed to be similar to the Basal nuclei, in its responsibilities involving repetitive movements, motor activity, and emotion. (I would give more information on differences here, however I currently do not have the resources for that much of bug stuff. Also I doubt that in real life they have feelings as such. This would be a good place to comment if I really do have any etymologists reading this).

Troll eyes very closely resemble those of humans, but in reality they are far closer to those of cephalopods. This is most obvious in the layers of the retina. In us, light passes through ganglion cells, bipolar (nerve) cells, and _then_ the rods and cones and then the impulse passes back the other way. Trolls have this layering inverted. It is unclear at this time how much of a difference this actually makes.

One difference that _is_ clear, however, is number of types of cones. Trolls have an additional type of cone at higher frequencies of light (it covers higher violets along with certain parts of the UV spectrum). It is unknown what these actually look like to a troll, but it’s said certain colors we’d classify as pink and purple are almost universally seen as “most beautiful” (although it’s unknown if that’s just cultural pressure, with these colors being associated with royalty).  

On the topic of the eye, it is my belief that trolls were not initially nocturnal. Their hierarchy relies too heavily on color and their living spaces (at least in the comic) seem to be fairly well lit, and they have no trouble cohabitating with humans. It seems likely to me that the expansion of their sun drove them to their current sleep cycle some time after the beginnings of civilization.

My other line of reasoning for this statement is in comparing grubs, which seem to have either translucent irises and sclerae or highly dilated pupils. These types of eyes would be useful in a very low-light environment, so it would make sense for the structure to remain similar in adulthood if the species is truly nocturnal. Instead, what we see is pigmentation after metamorphosis, with yellow sclerae and dark irises. This is likely to protect from the light that young trolls would be dealing with upon emerging from the breeding caverns. I believe at this time that the blood-pigments accumulate slowly over time. This might be a sexually selected trait (letting others know that the individual is ready to breed may have been beneficial), a form of hierarchical identification (knowing who was above or below may have prevented fights), or it could just be something that happens but was not found to be particularly harmful. 


	3. Endocrine System

**Notes for the Chapter:**

> Alright, so here’s the thing about the endocrine system: the author has a serious vendetta against the endocrine system. The main issue I have with it is the fact that there are a multitude of centers throughout the body that act mostly independently but are also all tied together through highly complex feedback loops. Due to the nature of this sort of relationship, along with the fact that the author hates it, this section will jump around probably the most of any in this work.
> 
> The other issue is about how much I haven’t learned about insect hormones. Part of the problem is that they’ve really only been studied in detail in a handful of species and the peptide (protein-based) hormones can sometimes be unstable. That being said, I will forge onwards and guess a lot. The good news is that I asked my professor and she gave me a lovely table that will help me fill in the blanks at least somewhat and it’s a made up species created by someone who is a metaphorical troll, so there’s no way to be completely right anyway.

The main endocrine centers in insects are the various parts of the brain, a prothoracic gland high in the thorax or back of the head, the ovaries (which we will get to later), and various centers along the ventral nerve chord. However, with a species like trolls that are so much larger and more complex than common insects, it seems likely to me that those centers along the nerve chord have specialized in order to meet the demands of increased size. These would likely fill some of the roles of the pancreas and adrenal glands (more on that in digestion and excretory, respectively).

Because of the fact that most of these centers are in the head and neck region, it seems logical (and really lucky) to me that hold some similarities to the endocrine glands in our heads. Earth insects have something called a corpora cardiaca (cc), which is a pair of glands behind the brain. These act similarly to the human hypothalamus and pituitary combination: creating, storing, and releasing various hormones. Because of the lack of space, in trolls these glands have grown closer and closer to the brain to the point where they can be considered one and the same, making the brain an endocrine organ as well as a nervous one. For the most part it does for the former what it does for the latter, in that it tells everything else what to do by releasing hormones that release other hormones (there are a shitton of these loops, which is another reason I hate this system). However, there are a few that act on their own, which I’ll mention here.

The first is called brain hormone. Apparently the creative scientists were all taking the day off. This talks to the CC, which then controls metabolism, heart rate, and other bodily functions. In trolls I’m guessing that there’s a wider range of hormones in order to control their more complex systems. Hell, there might be more in insects. As said earlier, there hasn’t been much in-depth research done on bug hormones.  

Oxytocin, or a chemical like it, is likely far more important in trolls than in other insects. This hormone is responsible for a good number of things, one of the most important in our case being bonding to other individuals. Trolls clearly form very strong attachments to others, which his highly uncommon in insects. In humans the release of oxytocin is tied mostly to sex and birth, but I believe trolls have a different sort of release mechanism. This is where papping comes in. There are likely sensitive spots on a troll’s cheeks, and gentle touches to these spots also triggers this release, which may help to explain why the bonds between those in platonic quadrants are just as powerful and important as those in concupiscent quadrants. (Also, pale masturbation, in which you pap your own cheeks, is totally a thing. As of now.)

Another one that comes up in humans over and over again is Vasopressin, or Antidiuretic hormone. Although again vague on its origins, my table mentions something called Antidiuretic Peptide that seems to do the same thing. If you’re into pharmacology, its primary use (conserving water) should be fairly obvious, and it’ll pop up again once we get to excretory. However, ADH (the human version) is also involved with raising blood pressure, releasing stress hormones, circadian rhythm, and possibly memory formation. So my guess is that it might take on similar roles in trolls.

Humans have something called a thyroid gland in their throat right beneath the voicebox. This is one of the primary glands for controlling metabolism. However, insects don’t have these (and the cc mostly controls metabolism anyway). What they have instead are things called prothoracic glands. These are a lot more fun because this is where the signal to molt happens, and molting is by far the most interesting part. (These glands atrophy during metamorphosis, allowing for the expansion of lymph tissues in this area and aiding in shaping the troll’s larynx).

If you’ve seen that gif of what looks like a crab popping out of another crab, that’s exactly what’s happening. Basically, as an arthropod grows there gets to be a point where they don’t fit into their exoskeletons anymore. This is when the prothoracic glands come into play. They create a hormone called ecdysone (so named because if you are cool you call arthropod molting “ecdysis”). It’s actually really cool and I suggest looking up videos of it. But basically what happens is the grub (because most molts do happen in the larval stage) gulps air until it splits its exoskeleton along a predetermined line. Where exactly this line is seems to vary among species. I’m debating where I want it right now. I feel like in the front would be most logical (it seems to be the most common among caterpillars), but I really like the idea of the grubs climbing to the top of the cave, popping out of their shells, flailing around, and falling back on the floor. Because there is a lot of flailing. I assume that’s because it’s like trying to get out of an article of clothing like two sizes too small. It’s just fun to watch.  

Then, in trolls at least, there is a lot of hiding involved. It takes a while for the new exoskeleton to harden up and get proper pigments in it. In the mean time, the freshly molted grubs are very, very vulnerable. On Alternia the brooding caverns are not a nice place, as will be explored in more depth once we get to reproduction and this is the point where the highest number of casualties occur. Trolls molt around once a perigee for the first sweep of their life, but luckily for them most hatched in the same clutch will molt at about the same time, so there are a fair number of survivors.

This pattern of growth-molt growth-molt continues for a long time (a sweep and a quarter in trolls). However, there’s one more hormone involved, known as juvenile hormone. This is made in a structure called the corpora allata behind the cc. Basically, its presence tells the bug not to grow up. (It’s also been called the peter pan hormone. I am not making this up.) As time passes, the amount of juvenile hormone decreases until it reaches a certain threshold, which triggers the metamorphosis.

We are also unfortunately vague on what happens during metamorphosis proper, which drove me crazy to no end. My best guess for the trolls themselves is that they’re unconscious for the duration. They climb to the top of the caverns (with the exception of seatrolls, who do it at the very bottom of their pools), spin their cocoons, and promptly pass out for a few perigees as their bodies rearrange themselves. They actually wake up smaller than they were when they fell asleep, but they have fingers and bones and a closed circulatory system, so that’s something. They then use their horns to break out of their cocoons.

At this point they still retain their grub legs. They’re often helpful for climbing walls and ceilings to avoid predators and enemies. Eventually the troll becomes too large to be supported by these legs, and they fall off at the beginning of puberty, usually leaving behind a set of scars. Around this time, juvenile hormone returns to play a role in reproduction. But we’ll get into more on that later.

For now, I hope you were somewhat able to understand this! We’re getting into cardiovascular (with brief mentions of muscle groups) tomorrow. So that should be more interesting. 


	4. Muscle and Circulatory Systems

**Notes for the Chapter:**

> So luckily for my time table (final is on Monday, aaaaaah), muscles are one of those types of structures that are highly conserved, so it can be combined with another relatively short section.

Muscle function in trolls is nearly identical to that in humans, and the majority of the muscle groups appear to have been put in the same basic place. The exception to this rule is in the midsection. Instead of having what we would think of as abs, the muscles on a troll’s stomach are quite thin in comparison to our own, with the stronger, weight-bearing muscles on the sides. This is partially believed to be a holdover, as the majority of Hussia walks on four or more legs. However, these muscles also serve important purposes for very young trolls, being what the grub legs are attached to. Having thin, elastic muscles at the front of the abdominal cavity also helps during reproduction, as they allow it to expand more quickly and make it easier for the troll to produce large amount of both genetic material and eggs without as much stress on the organs or the muscles themselves. Again, we’ll get to that later.

The circulatory system, on the other hand is somewhat more complex. Part of the reason for this is the large shift that happens during metamorphosis. As grubs trolls, like other insects, have an open circulatory system. What this basically means is that there’s basically one large tube running the length of the grub, with little holes called ostia along the sides, where hemolymph (not blood) can be returned to be pushed back towards the brain by the posterior heart. This hemolymph basically goes wherever it wants within the body, dispersing immune cells and dissolved nutrients, but not gasses. Instead, grubs rely on a duct system that allows them to absorb oxygen directly from the air (because of their fairly large size, to use this system grubs need to be kept in a high oxygen environment. Brooding caverns have always been filled with mosses and lichens to provide the much-needed gas).

However, this clearly changes by adulthood. The trolls clearly breathe, and the liquid in their circular system is blood and not hemolymph. This change likely comes about in order to give the trolls more freedom. A closed circulatory system results in more control and would allow adults to venture into areas with much lower oxygen levels.

During metamorphosis, the ostia close and the grub’s internal tubing begins to develop into a systemic-pulmonary circuit with a four-chambered heart similar to that found in mammals. This may seem highly improbable, but even on earth two very different taxa (cephalopods and vertebrates) have developed closed circulatory systems, and within vertebrates two different groups (mammals and birds) have developed a four-chambered heart. Therefore, this is likely one of the most efficient configuration for creatures with high energy demands. 

As trolls have true horns instead of antlers, blood is constantly pumped at least partway up (the reddest part has the most blood running through it, and by the time you get to the yellow there are almost no blood vessels). They have just about the same amount of feeling in their horns as we do in our teeth, but it gets weaker as we travel upwards. The majority of the cells within a troll’s horns are alive and the horns continue to grow throughout a troll’s lifetime in the same manner as a tree.

 Horns certainly play a role in sexual selection, and trolls generally take great pride in their horns, cleaning and polishing them on a regular basis. A good number of trolls file their horns to keep them a certain size or to obtain a certain look (this is especially common in trans individuals, smoothing off or carving in small hooks to appear more feminine or masculine, respectively. More on that later), and it’s not uncommon to have one’s horns engraved in the same manner as humans get tattoos.

Another topic that needs mentioning is the presence of gills in seadwellers. These gills are homologous to the ears of other trolls and there’s still a visible ear-hole in front of the gill (though their hearing is nowhere near as good as those of landdwellers. Normally this is not an issue, as sounds can carry much longer distances in water). However, even prior to hatching the gills become much larger with folded skin for higher surface area. During metamorphosis, these structures become highly vascular, improving their ability to absorb oxygen.

When relaxed, a seatroll’s gills are usually somewhat folded. When threatened, however, they can spread their gills wide for a more intimidating appearance. (Land trolls have similar control over their ears, being able to move them up, down, and backwards easily. When relaxed a troll’s ears are held fairly high, and when excited they twitch upward, though they cannot be held in that position).

There’s one thing, though, that still hasn’t been answered, and that’s the twice-mentioned “bladder based aquatic vascular system.” Hussie was probably trying to go for something like echinoderms, but since that contradicts the whole “having blood” part, we’re going to pretend that he didn’t. Within humans (and likely landdwellers) major veins (especially those in our legs) have one-way valves that help push the blood back up to get recirculated. This helps keep the blood from flowing back down towards our feet. Sea trolls take this up to eleven because they need to handle huge changes in pressure over short periods of time.

Divers probably know of the bends, which is basically what happens when you try to ascend too quickly after breathing underwater and the gasses dissolved in your blood turn into little bubbles. The result is similar to what happens when you try to open a shaken up bottle (usually if you get to a decompression chamber you can be taken care of, but otherwise it can be fatal). However, we see Feferi ascending and descending quite rapidly. This is likely possible because of this “bladder based system” being able to expand and hold the excess gasses until they can be reabsorbed or let out through breathing. Instead of having these bladders lining the vessels, it would make a little more sense for them to be accessory structures that still absorb the excess gas from the bloodstream. However, that doesn’t really make it bladder _based._ Do what you wish, but remember that Hussie and Paradox space like to say “fuck you” to parsimony.  


	5. Blood and Immune System

**Notes for the Chapter:**

> So this is topic I’ve actually been asked about. In troll culture, blood is pretty obviously a big fucking deal. I have a theory, but it’s a little complicated, so hold onto your hats. And for once I feel like I know what I’m talking about, so that’s good. It also means this probably has a ton of errors, but whatever. And I'm sorry for posting two in one day. I'm in hardcore prep mode.

 

Before we really get into the color, it’s important to talk about the basic composition of troll blood. Thing number one: they have red blood cells, as in erythrocytes that use hemoglobin. I toyed around for a while about perhaps having mixes of different sorts of oxygen-carrying compounds (such as hemocyanin), but found this less likely than simply having blood filled with pigments. Another thing is that, while mollusks and arthropods on earth use hemocyanin as a general rule, creatures who live in low oxygen environments often have hemoglobin instead (certain worms, and even a few arthropods). Also, it fits better with my understanding of Karkat’s mutation, which we’ll get to in a few moments.

However, one thing that’s important to mention is that these blood cells are nucleated. While mammal red blood cells are basically just big bags of hemoglobin, most other vertebrates have more complex ones complete with perfectly functional organelles. Therefore, these erythrocytes would act like any other nucleated cell (this will become important for understanding pigmentation). Because of this, their spleen is less important than it is in humans and they can survive without it, though they have much higher risk of certain types of cancers, as the spleen does still collect the red blood cells that just don’t quite work anymore.

Thing number two: they have specialized leukocytes, also known as white blood cells. Unlike most creatures, they have adaptive defense mechanisms. All animals have two innate lines of defense. The first is usually physical: skin and mucus, along with things like stomach acidity. This keeps out the majority of pathogens. The second like is a bunch of non-specialized cells that can take on things that are already inside, both pathogens that managed to make it through the first layer and also cancer cells. The second line of defense also includes things like fever and inflammation.

However, in addition to these two, in some vertebrates, along with Hussia (theoretically), there’s a third line of defense, which is the adaptive mechanisms. These are your antibodies (which, by the way, do not kill things but kind of lump them together and make them more conspicuous), and cells that are able to remember certain pathogens in order to fight better when you’re exposed a second time (this is why vaccines work). The actual mechanics of this are kind of complicated, but also pretty awesome (I suggest looking it up, though you may have to read through the material a few times to understand it). Anyway, the important thing is that vaccinations along with acquired immunity are things for trolls.

Other than that, the components of the blood are fairly similar to what you’d expect: they have some platelets for clotting, certain proteins that serve various functions, hormones, and a whole lot of plasma with salts and glucose and all that good stuff.

Trolls also have a highly developed lymphatic system, similar to humans (If you don’t know what this is, basically it’s taking the liquid that filtered out of your blood, cleaning it up, and putting it back in), though their lymph nodes are in slightly different places. They do, however, have something akin to tonsils in the throat.

Now that the basic stuff is out of the way, it’s time to tackle the hemospectrum. I’ve thought long and hard about where this comes from, and only recently I’ve come up with what I believe to be the most probable answer: the pigments are antigens. As some of my readers likely know, antigens are basically markers that let white blood cells identify self. The most well-known of these are blood antigens, which are what cause your blood type (if you have A antigens you have A blood, B you have B blood, both you have AB, and neither you have O). However, nucleated cells found throughout the rest of the body have antigens that are more complicated and unique.

Now remember when I said troll red blood cells are nucleated. Suddenly, if these two are combined, it starts to make sense that there’s so much variation in blood color within one species. This also means that blood color in and of itself is not actually tied to lifespan or abilities. However, individuals that are closely related will share many traits, including powers, land or sea, and metabolism (which translates in most cases quite cleanly to lifespan). As it so happens, these traits are all almost always inherited from the mother (I will not fully explain why until we reach reproduction, but now would be a good time to mention that trolls also produce eggs. It’s kind of in the same vein as the bladder based circulatory system, where I go “I see you’ve said that, but the way you’re planning to go with it makes no sense, so I shall adhere to the letter of the law instead of its spirit”) although the father can alter them slightly, making the offspring a tad higher or lower on the spectrum and sometimes creating unique powers.

When cells die, these pigments either detach or deactivate. This leads to things like the bright red color of Terezi’s eyes and allows for the headcanon of “troll tissues damaged beyond repair turn red.” Cells that have other pigments, like skin cells and hair follicles, retain their inner colors, which leads to the trolls not being brightly colored after their pupation. Think of tree leaves: they _look_ green, but once they die they turn red or yellow. Troll skin and hair is the same way.

So what the hell, you ask, is up with the vantases? To go back to the blood type analogy, think of them as like _super mega O,_ with no surface antigens at all. While they’re still coded for the limeblood power (FRIENDSHIP!), their horns are not the typical limeblood shape, instead remaining utterly undifferentiated (all of them start out nubby like that, but they normally differentiate by the time the eggs hatch). Other than the societal repercussions, this does not seem to have particularly affected their quality of life.

I’ve also decided that not adhering to the quadrant thing is probably a natural limeblood trait, wherein being the best moirail ever also often includes becoming the other troll’s everything. Because of that, it’s possible that instead of a full-out genocide, they ended up dying off because many of them refused to change to the required reproductive strategies. Of course, the government also might have gone “We’re losing some of our best subjects to these selfish assholes, let’s get ‘em.” Either way, it’s the quadrant system that eventually selected against them. 


	6. Digestive and Excretory Systems

**Summary for the Chapter:**

> I love conservation, yes I do, I love conservation because it means I can focus more on the stuff I actually need to be reviewing instead of going on long adventures in search of stuff about bug anatomy, how ‘bout you?   
> Some of my readers might find this chapter kind of gross, as it deals with, you know, all that comes with digestive and excretory systems. I’ve tried to be relatively tasteful, and there’s not actually all that much to mention about defecation, since it’s pretty similar down there. But here is your fair warning. But if you’re like me and you like the guts, you’ll probably be quite fond of this chapter.

So the digestive system is one of my favorites of all time because for the most part it’s very simple, very ordered, and there’s not a lot of stuff to memorize. Basically, in just about everything past like flatworms, you have a big long tube with some other things hanging off and many taxa have incredibly similar structures, because we all face similar challenges.   
The first thing to look at in digestion is what’s actually being eaten. My guess is that trolls are omnivores, though I assume meat is slightly more important for them than for us mostly because of their teeth and the fact that a lot of their foods seem to have the word “grub” in them. However, they have faygo, which means that they cultivate sugar, which means that plant farming is a thing they do. So they’re probably omnivorous.   
Insects typically rely on mandibles for chewing and tearing, but that doesn’t seem to be the case here. They likely possess fairly close analogues to vertebrate teeth. Their pointed front teeth may seem to be an indicator of a carnivorous diet, but we never find out what’s going on in the back. Since one of their primary food sources is obviously some sort of arthropod, it makes sense for them to have strong jaw muscles and flat teeth somewhere with which to crush and grind exoskeletons. It’s likely, then, that their teeth look something like a bear’s (though with a shorter jaw and smaller canines), wherein their front teeth are all rather sharp but they still have grinding molars in the back.   
Their saliva is fairly similar in composition to those of humans due to our (relatively) similar diet. The main difference is that in addition to normal salivary amylase (which breaks down most carbohydrates), they also have significant levels of chitinase after pupation. The grubs do not have this, as it is typically unfavorable to start to dissolve one’s own skeleton when attempting to groom (however, chitinase has no affect on skin, so forehead kisses on grubs, along with kisses anywhere on the body in adults are perfectly fine, though if one has young trolls and grubs in the same place, it’s best to discourage the young trolls from attempting to groom their younger friends like they used to).  
Adult trolls clearly have a pharynx, as they can breathe through their mouths. Therefore they have an epiglottis, or something like it, keeping things from going down the wrong tube.   
Really, we only get to the alien part when we get to the stomach. Instead of having one large bag like we do, troll stomachs are divided into the crop and gizzard. The crop basically just stores the food and gives the salivary enzymes a little more time to work. The tissue that makes up the walls of the crop is some of the stretchiest in the body, only outdone by the egg pouch in the female half of their reproductive track. This allows for them to eat a lot at once without their actual digestive organs being overwhelmed.   
The crop also came in handy during the time period where parents raised their own grubs. Like many creatures that feed their young but aren’t mammals, regurgitation was the primary feeding method for a long time (especially because this allows for the young to absorb nutrients from exoskeletons). If left to their own devices, grubs will instinctively knead (ideally on their significant adult’s stomach, but in the brooding caverns they find all kinds of interesting things to do it to) to attempt to promote this. But eventually people decided that was kind of gross, so the grubs are instead fed rotting meat. Which method is actually more disgusting is left up to the reader (especially considering that we feed our babies modified sweat. Come on now, life is just nasty no matter your phylum).   
A troll’s gizzard is a lot more similar to what we would expect of a stomach, although it’s a lot less willing to expand. This is where hydrochloric acid and pepsin really come in to do their job and where we see the characteristic churning motions, provided by a special layer of muscle not found elsewhere on the alimentary canal.   
Past that point the differences are minimal. Much like in mammals, trolls have massive amounts of bacteria, fungi, and all kinds of cool stuff like that living in their large intestines. This helps them to further break down certain compounds. These microbes are usually obtained in the brooding caverns, because they’re not actually cleaned like ever. As such, trolls who survive the danger and disease emerge with very hearty immune systems and a thriving ecosystem in their gut. This kind of early exposure is believed to be one of the reasons for the low rate of allergies and auto-immune diseases in trolls (well, that and the fact you can be culled for it, but that is neither here nor there).   
While insects do not have pancreases or livers, trolls have structures that are almost perfect analogues for those found in humans. The primary difference is that the liver is smaller and the gallbladder larger. They also have what is essentially a second gallbladder to store pancreatic juice (and keep it in its inactive form). This is because for much of the history of troll kind, there was a lot of highly irregular feeding. Their bodies are designed to be able to fast for a long period of time, rapidly digest large amounts of food, and then store the energy for later. However, it has been found that this kind of behavior puts extra stress on their digestive systems, and that a fairly consistent, though varied, diet tends to be the healthiest. Just keep in mind that a balanced diet for trolls is one significantly higher in meat and lower in vegetables than a balanced diet for humans.   
The excretory system, on the other hand, has some very significant differences when compared to us. For one, they lack what we would consider kidneys. Insects have malpighian tubules, which are these little tubes that do the same job of filtering, in their case, hemolymoph and creating urine. Instead of being separate from the digestive tract these are connected at the junction between the midgut and hindgut (what we would call small and large intestines).   
Trolls, evolving from insects, have the same basic setup. However, these tubes are longer and branched, threading through the small intestines. They come into close contact with many blood vessels this way and the slow movement to the base gives water and needed electrolytes time to filter out. By the time the base of the tubule is reached, most of what’s left is toxins, salts, and uric acid (which is not created within the tubules, but is one of the wastes filtered out by it). These are then dumped into the large intestine to have even more of the water removed before being expelled with everything else.   
So basically, trolls don’t pee. The fact that humans do (and the fact that it comes so close to reproductive organs, in human males using the same fucking duct) is incredibly disgusting to them. You should have seen it when Dave explained watersports. There was fun for all, except for Karkat who nearly imploded.


	7. Reproduction

**Notes for the Chapter:**

> So here we go, the final chapter and the one that’s going to be the most controversial (partially because of social justice stuff, but mostly because there are about 10 billion troll sexcanons). You may be going “But Char, what about respiration?” Well, I looked back at my notes yesterday, and there’s not much to say on the matter. What little is noteworthy will be worked into this chapter.

 

The biggest challenge in describing the full nitty-gritty cycle of troll reproduction is describing the difference between gender and sex characteristics, since trolls identify by the same genders we do, but have both male and female sex characteristics. To describe this we basically just have the words ‘male’ and ‘female’ which are ripe with connotations that simply do not apply in this case (Again, my apologies to any readers who are trans, non-binary, genderqueer, or anything other than cis. I’m doing the best I can to balance political correctness with biological accuracy. This is the constant struggle of my life). I believe that the best way to do this is talk about the development of gender followed by sexual organs. This will be fairly easy to do if we begin with grubs hatching from eggs and then continue through development. For the sake of this chapter, ‘mother’ refers to the parent that made the egg and ‘father’ refers to the parent that fertilized it regardless of gender (they can even be the same individual, as trolls are capable of self-fertilization, though the offspring tend not to be as healthy).

I also believe that there is a difference between what is natural for trolls and had happened throughout most of their history and the practices we see on Alternia. I will point out these discrepancies as they appear throughout this chapter.

A troll egg that’s ready to hatch is approximately six to seven inches in diameter. Its shell is soft and translucent, tinted its mother’s blood color. The grub is curled in a way we would think of as backwards, so that the horns are towards the center and do not puncture the shell. As their teeth develop and the yolk starts to run out of nutrients, grubs will begin eating their egg shells from the inside. Eventually, they chew through completely and hatch. Their horns, which had been kept somewhat soft in the fluid environment of the egg, harden within an hour, aided by the grub instinctively grooming itself. They are able to run and hold their heads easily within half an hour of birth, which is especially good in the Alternian brooding caverns as older grubs will be attempting to hunt them (it’s not quite as big of a deal in more natural settings, where the parents will usually protect their young).

Grubs go through a sweep and a half of life in their grub stage, eating and molting on a fairly regular basis. Grubs must be kept in high oxygen environments because instead of possessing lungs they rely on a tracheal system to perform gas exchange. Basically, this means that they’re full of these tiny little holes called spiracles that attach to a complex duct system. By the time an individual is ready to pupate they would suffocate on the surface because they just can’t get enough oxygen to their cells.

Throughout most of Alternian history, parents would collect a ridiculous amount of plant matter with which to fill the nursery block. Eventually, oxygen machines were invented, which made it a whole lot easier. Then, upon the foundation of the current regime, the grubs were taken to large caverns naturally covered in mosses and lichens. Historically, grubs would be fed by their parents in the same manner birds on earth feed their young and are paid very close attention to. In the brooding caverns, however, they’re mostly left to their own devices. The grubs are given less than enough food necessary for survival so they have to fight for it, and what they are fed is incredibly subpar. This is meant to encourage murder and even cannibalism. (The Mother Grub does provide some protection, but only from those outside of her clutch).  The vast majority of Alternian grubs meet their end either by starving to death or being hunted by their siblings.

Until pupation they are treated mostly by adults as non-entities on Alternia, neither given names nor assigned genders (though part of the latter is explained in a moment). In non-cavern circumstances they _are_ named and a special pronoun is often used to refer to them. They are, however, intelligent at this point. They have been shown to be able to solve complex problems in laboratory settings, and in the caverns often form alliances for protection. Grubs raised in family situations are often observed showing empathic behavior and grieving if a sibling is lost. These behaviors are less frequently observed in the brooding caverns, though the cause is uncertain. These behaviors could have been bred out of them by the environment, they may hide it purposefully to avoid being targeted, or they may simply be too traumatized. No matter the environment, trolls also begin learning about adult troll behavior during this stage. Normally this usually just means copying the parents. Grubs in the brooding caverns are shown instructional videos with bad rap music in the background.

At about one sweep old, they start to be told about pupation and understand the importance of where they choose to spin their cocoons. Trolls can be thought of as exhibiting a form of protandry, which is to say they’re all born as male (though no sexual characteristics whatsoever are present in grubs). Young trolls let out a progesterone-reducing pheromone (partially to keep their parents from ovulating when they’re too young). If a grub pupates closely to others, they will emerge as male because of this. If they go on their own, however, they do not feel the effect of these pheromones and emerge as female.

The differences between the two, however, are very slight at this point of time (the only difference is the horns mentioned previously). The decision of gender is easily reversed up until puberty in modern society, as there are drugs that can turn the switches set during pupation on or off (though depending on how late the decision is made the troll in question can still appear more masculine or feminine).

This sort of gender determination also leads to many intersex individuals, who either placed their cocoon to close or too far away from a group to fall neatly into one category or simply couldn’t decide. Sometimes they choose a binary gender to present as, sometimes not. It depends on the individual (I headcanon Terezi as being like this, and Equius either like this or having an above situation where he changed his mind. In the case of the Signless, the Vantases may lack the proper machinery to turn female. That or he was allowed to pupate near others somehow).

It is at this point that Alternian trolls face the trials and, if they succeed, receive a lusus. Regardless of regime, the next few years are full of fairly slow and uniform development, though slight differences begin to appear. Females often find themselves bigger and heavier than their male counterparts, as their bodies are built to be more combat-oriented. Females are incredibly sturdy and full of muscle surrounded by a protective layer of fat (thicker around the hips and chest to protect vital organs). After puberty, breasts especially serve as signs of strength. The larger the bust, the more likely the female is to have thick protection elsewhere, so it may be best to avoid a fight. Females are often more territorial and aggressive, though how much of this is a result of hormonal differences and how much is simple socialization is widely contested.

Males, on the other hand, are made for speed and agility. They’re usually lighter and slimmer than their female counterparts. Traditionally, they would serve more administrative roles as they’re stereotypically calmer and more analytical than females (which is why in Beforan and Alternian society they seemed to have capitalized on places of legal power). They’re also historically more involved in raising grubs (the Jadebloods are female because their job is to protect the mother grub, not actually to take care of the babies). Their secondary characteristics, extra hair and deeper voices, are made to make them seem more comforting to young trolls. Their thinner abdominal protection also makes it easier for grubs to induce the feeding reflex.

When it comes to trolls exemplifying these traits, Vriska is probably the most feminine troll we really get to know (though Nepeta is a close second). Tavros is the most masculine, though he tries to break out of that role (when his cards are referred to as ‘games for girls’ it’s because they focus on the fighting portion. Tavros is almost perverting it by making it more about the breeding. This makes many trolls uncomfortable, but fuck them.) The Signless as he is often portrayed would be a great example of adult troll masculinity, while the Empress is naturally the most girly girl of them all. (I have a lot of troll gender feelings).

Now comes the fun part: actual reproduction. From this point on, unless otherwise noted, when I use the word ‘female’ I mean ‘the bit that makes/nurtures the eggs’ and when I say ‘male’ I mean ‘the parts that make/release the sperm.’ Just because there aren’t really other terms that usefully concise.

When not being used, all troll reproductive organs are internal. Both the bulge and the nook are hidden behind the bonesheath (though the tissue over it is still more sensitive than most, which is why it hurts Gamzee so much when Kanaya kicks him between the legs). This can open half way (to just reveal the bulge) or fully to allow access to the nook. The former is more common in blackrom, as nooks tend to be more sensitive and easily damaged (though bets are normally off during ovulation).

The male portion of the anatomy has much analogous to our own. However, the structure of their bulge is very different from that of a penis. It’s made of several long, dexterous tentacles, the number corresponding to blood caste (redbloods have one, orangebloods have two, and so on until you get to the pinks which have eight). However, there is always one primary tentacle that releases the genetic material. In male-female intercourse the others typically aid in stimulating that base of the partner’s bulge, as well as pulling out genetic material from competitors (the reason that higher castes have more is they tend to be less fertile than others, so more clearing of rivals’ material is helpful).

The testes are internal and about the same size as those found in humans. They also release about the same amount of sperm. There are other glands along the way that add things like fructose and pH buffer to help keep the actual genetic material alive. One interesting note is that troll sperm is also full of macrophages that are specifically programmed to target sperm and other macrophages. The rest of it is water, which normally helps for two reasons. It can help wash the competition away and it also distends the uterus/genebladder/egg pouch/whatever you want to call it, which further stimulates it (unless you’re on Alternia, in which case it ups your output volume and makes you less likely to be culled). The reason that there’s so much made for clearing away other seed is that the quadrants really come into play here. When not breeding, only the matesprit typically has nook access, but when a troll is in heat they’re generally open to any of their quadrants (even auspices may abandon their post in order to attempt to breed). The kismesis especially takes advantage of this, and they usually release genetic material richer in sperm when their partner is ovulating (they tend to tie in terms of total numbers of offspring with the matesprit, who’s no more potent but often gets the most chances).

When uterus (which is the term I’m going to use) is stimulated enough, it sends a signal to start producing eggs. About 100 eggs mature in the troll’s ovaries for about two weeks, at which point they slide down into the uterus. If fertilized by genetic material, they remain and continue to be nourished by the mother’s body.

The method used on Alternia is designed to get as many trolls as possible with the least amount of effort by the adults. This is done by artificially changing the site of fertilization in order to make trolls more r-selected than they naturally are. The empire insists that the eggs be given unfertilized. They give two weeks’ warning and by then you’d better have a bucket full of eggs. To accomplish this, matesprits stimulate each other heavily, but pull out to release (this is _supposed_ to be thrown away, but some save it to cheat the system). When unfertilized, after the two week maturation period the eggs are just released. If kept at the mothers’ body temperature and surrounded by nutrition slime they can be kept viable for some time more. These eggs go into the matesprit pail.

The kismesis is required because their sperm is more potent and able to last longer (during ovulation, matesprits often go quantity over quality). This is what goes in the other pail. There are many ways to cheat this system, including hiring temporary partners, switching quadrants (a good moirail can easily act as a matesprit for that time, and an auspice will step back and allow the kismesis to develop for the sake of their partners’ survival), or simply double dipping as mentioned above. However, if the bond is not strong in the proper quadrants, the gametes tend to die more quickly and are less likely to form viable grubs. Of course, this system doesn’t care about how many offspring are unviable. They simply need the quantity because most of them are going to die anyway. Removing the gametes from the parents in this way allows for more random variation and also for them to be out of combat for two to three weeks instead of over a year.

The mother grub is then injected with the eggs and the semen and nourish them for a while. However, instead of incubating for six perigees they only do it for four. After the mother grub lays these troll eggs, they are further incubated and kept in nourishing slime.  

It makes little sense to me for the mother grub to be the same species as the trolls. I am aware that extreme sexual dimorphism is possible, but in this case it would cause some serious gender confusion. If the mother grubs are actually just the female form of trolls, why then do trolls sort themselves into genders? They could be a three-gendered race, but then why assign female pronouns to the mother grub as well? Furthermore, it just doesn’t seem like a likely evolutionary system to me that two individuals have to have sex to then externally fertilize a very different female no one has any attraction to. Not impossible, but kinda weird and somewhat unlikely. (Also, I doubt that all trolls would hatch out of something like the matriorb, although trolls would certainly not be the only species that requires males to produce more males and otherwise makes females).

In the more natural system, once the eggs are fertilized they embed in the uterine wall. From there, the elimination begins. Many of these fertilized eggs simply die from mutation or genetic defect (there are more errors due to how many gametes are made so quickly). Others are not accepted by the mother’s body for various reasons and also die. More are eventually just reabsorbed because the mother simply can’t support that many eggs. Whatever the cause, the vast majority of these eggs are killed off. Out of the 100 or so unfertilized eggs, by the end of the six month incubation period only from about three to seven eggs (depending on caste) remain, though they’ve grown from their original inch diameter to about five to six inches (they further stretch another inch while they wait to hatch). The mother’s size typically skyrockets during ovulation, shrinks when the embryos start to die, and then they swell up again as the eggs get close to mature.

The eggs are then laid. At this time the grubs lack hair and legs and have only tiny nubby horns. In about a perigee and a half, the grubs are fully developed and ready to start the cycle all over again.

Trolls on Alternia know well of this form of reproduction (since otherwise how would they know what can go wrong if you come inside your matesprit?), but are raised to think of it as disgusting and an awful, terrible thing to happen to your body. And then that you’d also be killed. It’s taught to them as primitive and disgusting, like we’re taught to feel about all practices of medieval life. Much like medieval life here, there are some trolls who do romanticize the idea, but not enough to actually do it. Or if they do they are either killed when they can’t deliver material for the mother grubs or their own offspring suffocate or are killed accidentally. 

**Notes for the Chapter:**

> I think, then, that this is the end of the Complete Guide to Xenobiology. I have come up with all I can think of to say on the matter, but don’t be afraid to continue asking questions! Question all the things, and I will be happy to respond! If there’s enough I ended up missing, I can even post an auxiliary chapter. I hope you all enjoyed it and understood most of by babbling.


End file.
